Which Bonus Power for an Engineer on Insanity mode?

Which bonus power would be best for an engineer class on an insanity play-through or is it better to take a different class and if so what class/Bonus power should i take? And does anybody have any advice on the best way to approach an Insanity play-through? And what things would make it easier to do? Any advice would be greatly appreciated

Lets take a look at each bonus power and break it down individually:

Ashley (assuming she's alive):

• Inferno Grenade: Not a bad choice as the engineer class doesn't have any grenade powers. Really useful to flush enemies out from behind cover.
• Marksman: Boosts accuracy and fire rate of your weapons, but an engineer is more focused towards powers so not that useful.

James:

• Fortification: Provides defense and melee on purge, but slows power recharge by 60% (can be reduced to 30%). Although survivability is nice, an engineer relies heavily on power spamming so the slowdown on recharge is a big killer.
• Carnage: Very high single target damage, can even stagger Atlas mechs. Pretty useful skill in a pinch, does high armor damage, but incinerate also does high armor damage.

Kaiden (only if he survives virmire):

• Barrier: provides defense at the expense of power cooldown just like fortification, not really a good choice imo.
• Reave: Insanely useful as the only other way to recover health is to use a med-gel.

Garrus:

• Armor Piercing Ammo: Since the engineer doesn't have an ammo ability, and the majority of big and tough enemies in the game high high armor, this is an excellent choice to take.
• Proximity mines: Very handy if you can lay down a lot prior to an engagement. Enemies tend to be more aggressive and mobile on insanity so this isn't a bad choice.

Liara:

• Stasis: Holds a single (non armored) target in place for a long time. Okay ability, not too useful imo.
• Warp ammo: One of the best ammo powers imo, grants high damage against everything.

EDI:

• Defense Matrix: Same with fortification, reduces power recharge as a trade off for survivability.
• Decoy: I never played around with this much, so I can't say either way if its effective or not.

Tali:

• Defense Drone: Having an additional target on the battlefield is always handy. Fully upgraded drones also have a handy AOE effect in chain lightning. I like this skill a lot.
• Energy Drain: Does massive damage to shields and barriers while recharging your own. This is a great skill to have since it provides survivability without suffering power cooldown penalties. This is a good alternative to overcharge.

Javik: I don't have him so I'm leaving him out.

In conclusion here are the good ones to consider:

Reave/Energy Drain for survivability
Defense Drone (and possibility decoy) for an additional target
Warp/Piercing ammo for an ammo power
Inferno Grenade/Proximity mine for something different

I fully disagree with Marshal Shepard's assessment or the engineer being too squishy for insanity. My favorite class is the engineer and I have completed ME2 multiple times on insanity and ME3 once on insanity.

First, the ability to double your squad size with a combat drone and a sentry turret within the first 6 seconds of an engagement is unmatched. Because the Mass Effect AI forces the enemy to deal with drones first both of those abilities enable you to get inside the enemies decision making cycle and thus influence the battlefield on a major scale. So while your squadmates are taking advantage of the chaos the engineer just created, the engineer can either assist with target engagements or continue to influence the fight through continual spamming.

Second, incinerate is one of the most powerful and effective powers available. Not only does it deal massive damage, but it damages every level of protection, including regeneration. Add to this the "panic" effect and once again the engineer influences the fight by interruption the actions of the enemy.

Third, overload is now more powerful than ever in Mass Effect 3 since warp has been changed to no longer strips barriers, and overload has been changed to strip not only shields, but also barriers. Now, not only does overload strip valuable protection, but it stuns opponents and overheats weapons. With these changes to overload in ME3 energy drain is somewhat superfluous. The engineer now must decide if they would rather have the weapon overheat effect of overload, or the draining effect of energy drain.

Fourth, cryo blast although not damaging allows the engineer to remove enemy numbers from the fight by snap freezing them. In the sequence of a battle by the time the drone and turret have been on the field long enough to strip shields and barriers the engineer can begin freezing opponents thus providing easy targets for the squad.

Fifth, sabotage is the only power available that will turn the enemy against itself. Assuming control of a turret, Geth Prime, cannibal or marauders is an extremely effective way of reducing the enemy force while conserving your own. If done properly, the engineer can add 3 members to the squad; a combat drone, a sentry turret, and a sabotaged enemy.

Sixth, because Mass Effect does not differentiate specific armor types by class, the engineer is able to wear the same level of armor as a soldier. Add to this the ability to modify armor and select bonus powers and upgrades and an engineer's health and shields will surpass and can rival any member of the squad.

Finally, once again because Mass Effect 3 no longer differentiates specific weapon types to specific classes, the engineer is able to carry a high damage assault rifle such as the Mattock or high capacity sniper rifle such as the Raptor. Thus the engineer is able to engage and destroy targets at any range and at any point in the combat sequence.

When compared to the most common player strategies of cloak-shoot-repeat, charge-shoot-repeat both which force the player to target a single enemy at a time, the engineer's strategy of drone-turret-overload/incinerate allows the engineer to target 3 opponents within 6 seconds, tying two of those opponents up for prolonged periods.

This analysis, I believe demonstrates not how squishy the engineer is, but rather how powerful and useful the engineer actually can be even on insanity level.